MEMS devices are based on using microelectronic wafer fabrication techniques to produce complex shapes in the μm to mm size range with embedded sensors, actuators and circuitry. Microelectromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices. MEMS devices are potentially low-cost devices, due to the use of microelectronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
Micro power generation techniques known in the art include thermo-electric converters, micro combustion engines, micro fuel cells, and micro fuel reformers. Hydrocarbon fuels offer attractive alternatives as power sources due to their superior energy densities. For example, the energy densities of propane, methane, gasoline, and diesel are at least 50 to 100 times higher than the best lithium-ion batteries. Typical solid propellant has an energy density of around 5 J/mm3. Commercial Zinc-air batteries have an energy density of just 3 J/mm3. Commercial lithium batteries have an energy density of only 0.3 J/mm3, and gold capacitor has an energy density of 9 J/mm3. Accordingly, the conversion of the chemical energy contained in the solid propellant to useful energy would provide a micro scale combustion device that would be competitive with commercial batteries.
Microthrusters are also known in the art, primarily for the use with propulsion of micro satellites. These systems deliver great force and are too heavy for micro satellites. Also the configuration is relatively complicated and expensive to make. The main applications for the micro thrusters are high accuracy station keeping and attitude control of micro-spacecraft.
It is known in the art that magnetohydrodynamic (MHD) technology has the potential to obtain the lowest cost of electricity with the highest efficiency. The MHD principle is widely used for pumping of liquid and in the metallurgical industry. The idea is now also seriously considered for ship propulsion using the saline seawater as the conducting medium to drive ships. This is a particular interest for submarine propulsion because of the potentially noiseless operation of such an MHD drive using a liquid medium. The rapidly increasing demand for energy throughout the world cannot be sustained without a substantial reduction in the environment and thermal pollution that would be associated with such demand. MHD conversion technology offers a remedial solution. MHD generators are extremely efficient and provide a direct and clean conversion of heat energy to electricity. Magnetohydrodynamic technology will play a critical role in the future fight to bring under control the negative environmental impact of expanding power demands.
The field of MEMS grew out of the integrated circuit industry. Initially, layered silicon microstructures were fabricated. These structures evolved into single function sensors and actuators that were then combined into systems with integrated circuit controllers. Currently, macroscopic power supplies are being used to power these microscopic systems. What is needed in the art is the integration of the micro sensor and actuator systems currently known in the art with an effective micro power supply.
To date, the primary focus of MEMS has been on sensors, actuators and specific applications of the technology. One area that has been largely neglected is how to provide power for microscopic sensors and actuators. The development of a power supply that is equal in scale to the sensors and actuators currently known in the art will permit local control of each component through an independent power supply, thus reducing the overall complexity of the control system. Advantages in terms of efficiency and speed of operation will also be realized.
Therefore, there exists a need in the art for a micro power generation devices for use in microelectromechanical systems.